This allowed broadcasters to present a political opinion or point of view or pundit without being required to allow equal time for alternative views or rebuttal.

At the same time, AM radio was languishing in the shadow of the higher quality sound of FM, with no remarkable content to attract listeners.

Into this perfect storm of opportunity rode Rush Limbaugh, with his brand of outlandish self-depreciation and mockery and conservative positions. He has since been followed by many other more or less successful pundits; likewise the millions of listeners Limbaugh attracted to Talk Radio led to the creation of the Fox Radio Network.
Liberal talk radio has been rather less successful.

Sean Hannity

Rush Limbaugh

Bill O'Reilly

Michael Savage

Michael Savage, birth name "Michael Weiner", pronounced wuy-ner, born in 1942 is an independent, mostly non partisan conservative talk show host who is now best known for being banned from entering the United Kingdom in May of 2009 over debunked accusations of hate speech and "inciting racial hatred", all of which are proven to be false.